Yanmar 3YM20 Mixing Elbow

[davenrino]

I have a 2018 Yanmar 3YM20 with 200 hrs and it recently started revving to 2400 instead of well over 3000 going forward while still getting to 3500 in neutral. I am thinking the original exhaust mixing elbow may be restricting flow. It came with the u-shaped riser like this HDI replacement -
https://hdimarine.net/product/ymkit/






Is there any reason not to switch to the straighter replacement at half the cost? -https://hdimarine.net/.../yms-stainless-steel-mixing-elbow/

[gonesail]

i heard 600 hours as replacement schedule for the mixing elbow. but maybe yours is ahead of schedule. are you getting any steam in the exhaust?

[davenrino]

Originally Posted by gonesail

i heard 600 hours as replacement schedule for the mixing elbow. but maybe yours is ahead of schedule. are you getting any steam in the exhaust?

No steam but some black crud on the water and a small puff of black smoke when backing off the throttle.

[Tin Tin]

Why not just take it off and clean it and inspect, not hard to do. You may also have a fouled propeller or bottom. The reason for the high lift elbow is usually to get the elbow higher above the water line, depends on your situation on whether to use low rise or high rise and if you have an anti-siphon loop from heat exchanger to elbow.

[davenrino]

Originally Posted by Tin Tin

Why not just take it off and clean it and inspect, not hard to do. You may also have a fouled propeller or bottom. The reason for the high lift elbow is usually to get the elbow higher above the water line, depends on your situation on whether to use low rise or high rise and if you have an anti-siphon loop from heat exchanger to elbow.

That is the plan for tomorrow. I already went under the boat to check for fouling.

[NorthCoastJoe]

You want that vertical section to be so that the raw water injection point is 12 inches above the water line. I like to make it as high as there is room within reason.

That prevents water from flowing back into the engine from the muffler. Unless your exhaust manifold is 12 inches above water line I would not do the cheap one unless you want to be buying a new engine in the future.

[davenrino]

Originally Posted by NorthCoastJoe

You want that vertical section to be so that the raw water injection point is 12 inches above the water line. I like to make it as high as there is room within reason.

That prevents water from flowing back into the engine from the muffler. Unless your exhaust manifold is 12 inches above water line I would not do the cheap one unless you want to be buying a new engine in the future.

Expensive one ordered.

[cram]

Have you tried changing the fuel filters and removed/ inspected it before ordering anything expensive?

[davenrino]

Originally Posted by cram

Have you tried changing the fuel filters and removed/ inspected it before ordering anything expensive?

Fuel filters 3 months ago with annual service. Pulled exhaust mixer today and it is soaking in muratic acid.

[Tin Tin]

Originally Posted by davenrino

Fuel filters 3 months ago with annual service. Pulled exhaust mixer today and it is soaking in muratic acid.

Hope that is pretty diluted, the internal metal tubes are not that thick. Less corrosive acids are Phosphoric or Oxalic for this sort of work, IMO. I have not actually used an acid to clean them, just wire brush and then tapping to knock the soot out.

[MCilenti]

Just a note that if you do replace the exhaust elbow, I very highly recommend HDI.

The quality of the components is exceptional as was their customer service. I was also pleasantly surprised the stainless steel elbow was cheaper than Yanmar's cast iron.

We replaced our 3GM30-F exhaust elbow and added a new heat blanket from them a couple of years ago. Everything fit as if it were OEM.

I'm in no way compensated by HDI, it just seems rare to find a company with good products and good people anymore.

Cheers,
Mike

[cram]

Originally Posted by davenrino

Fuel filters 3 months ago with annual service. Pulled exhaust mixer today and it is soaking in muratic acid.

OK, but they can still get clogged if you have bad fuel, which would limit fuel flow and rpm....

Was the mixer obstructed much?

[Rohan]

Is there any reason not to switch to the straighter replacement at half the cost? -https://hdimarine.net/.../yms-stainless-steel-mixing-elbow/

When I had to replace mine on my 3YM30, I also considered switching, but I didn't. If I understand correctly, the rising elbow is considered to be safer to keep water from coming through the exhaust pipe and into the engine.